Are You Confident of the Diagnosis?

Characteristic findings on physical examination

The diagnosis of Confluent and Reticulated Papillomatosis of Gougerot and Carteaud (CARP) is based on slightly scaly, often hyperpigmented, very thin, elongated plaques as well as papules that coalesce into plaques on the upper trunk and flanks. It can involve the neck, face and groin (Figure 1). The highest prevalence is in adolescent/young adult age.

Figure 1.

Note hyperpigmented scaling plaques in a digitate pattern on the flank.

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Expected results of diagnostic studies

Negative potassium hydroxide (KOH) test rules out tinea versicolor but positive KOH can rarely be seen in CARP likely due to incidental fungal element in the skin. A fungal culture must be specially plated with lipids because the Malassezia yeast implicated in tinea versicolor cannot be grown in the laboratory using standard fungal culture protocols.

Diagnosis confirmation

The distribution is beyond the posterior neck and axillary vaults as seen in acanthosis nigricans (AN). The reticulated, finger-like projections on the flanks are typical of CARP and not seen in tinea versicolor or AN. In dark-skinned patients there is typically hyperpigmentation with the scaling; however, in light-skinned patients this may be absent. Biopsy may just look like normal skin with slight papillomatosis so the pathologist should be alerted and fungal stain should be performed to rule out tinea versicolor.

Who is at Risk for Developing this Disease?

CARP is almost exclusively a disease of postpubertal young adults. It is more easily recognized in dark-skinned people due to the hyperpigmentation but is likely under-recognized in light-skinned people. It is more common in women in the USA but is more common in men in Japanese literature. CARP may be more common in obese patients and those with endocrine disorders such as diabetes mellitus.

What is the Cause of the Disease?


There are multiple theories for the pathophysiology and etiology of CARP. CARP has been described more commonly in patients with endocrine disorders such as diabetes mellitus and thyroid disease. Theories for the pathogenesis are listed below.

Abnormal keratinization

The histologic hallmark is epidermal thickening with abnormal keratinization with melanosomes, leading to the look of hyperpigmentation. This may be primary or secondary but would explain the response to retinoids and possibly topical vitamin D derivatives.

Bacterial infection

There are reports of both Dietzia species (an Actinomycete) as well as Staphylococcus aureus but other reports have failed to find organisms on staining of histopathologic specimens

Infection would make the most sense based on the response to oral and topical antibiotics, which are typically the most effective therapies; however, tetracyclines are also anti-inflammatory and this may be their primary effect in CARP.

Fungal infection

There are many reports of isolation of Malassezia species from patients with CARP but this is not likely to be the only cause because therapy with antifungals is often ineffective. KOH-positive yeast (Malassezia species) can be found but may not be pathogenic as this is a common colonizer, especially in post pubertal people. Tinea versicolor may be confused for CARP clinically.


There may be a genetic predisposition, as CARP can run in families, but this could also be observed if there was an infectious or environmental cause

Systemic Implications and Complications

CARP does not lead to any systemic disease but may be associated with other systemic diseases. Obesity, diabetes mellitus, and immunosuppression have been sporadically noted in patients with CARP. Since AN and tinea versicolor are both seen more commonly in obese patients and can clinically mimic CARP, these associations may be overstated. There has been some correlation with immunosuppression but this is not consistent; as long as there are no other red flags, a workup for immunosuppression is unnecessary.

Treatment Options

The option of no therapy is reasonable given that this is a cosmetic disease.

If therapy is pursued:

Oral antibiotics

These have the best evidence for efficacy:

Minocycline (50-100 mg daily to twice daily)

Doxycycline (50-100 mg daily to twice daily)

Tetracycline (250-500 mg twice daily)

Erythromycin derivatives (clarithromycin, azithromycin and erythromycin at typical anti-infectious doses)

Topical antifungals and antibiotics

These have some evidence for efficacy in the therapy of CARP but are also low risk and would treat tinea versicolor if there is any question about the diagnosis:

Topical antifungals (ketoconazole 2% cream, miconazole 2% cream, clotrimazole 1% cream, selenium sulfide 2.5% lotion or 2.5% shampoo)

Topical antibiotics (mupirocin 2% ointment)


  • Topical tretinoin 0.025%, 0.05%, 0.1% creams, 0.025% gel each evening

  • Oral isotretinoin 0.5-1 mg/kg/day divided twice a day should be reserved for severe, biopsy-proven and recalcitrant cases


  • Topical vitamin D analogs (calcipotriene and tacalcitol) each twice daily

Optimal Therapeutic Approach for this Disease

CARP is not dangerous but is often cosmetically disturbing.

In children over 8 years old and those with their permanent teeth, oral minocycline has the most consistent evidence for efficacy and is usually first line. Minocycline has risks, including drug-induced lupus, severe drug hypersensitivity, Stevens Johnson syndrome, drug pigmentation and pseudotumor cerebri; however, typically minocycline is well tolerated. Doxycycline or tetracycline are reasonable alternatives, although with less evidence to support their use. They have fewer severe side effects and likely have similar activity.

Topical antifungals may have some limited benefit but are generally safe even in children; therefore, they are a reasonable option when the diagnosis is in question or if tinea versicolor cannot be ruled out. Topical retinoids, mupirocin, and vitamin D analogs have limited data to support their use but are low-risk medications. Oral isotretinoin should be reserved for recalcitrant and biopsy proven cases.

Patient Management

Follow-up in 4-6 weeks to monitor for benefit and/or side effects of prescribed medications. Recurrence can occur after discontinuing therapy.

Unusual Clinical Scenarios to Consider in Patient Management

Be careful to differentiate between widespread and acute onset acanthosis nigricans. which can be a paraneoplastic syndrome, especially when it does not respond to therapy directed at CARP.

What is the Evidence?

Baalbaki, SA, Malak, JA, al-Khars, MA. “Confluent and reticulated papillomatosis. Treatment with etretinate”. Arch Dermatol. vol. 129. 1993. pp. 961-3. (This article describes the use of etretinate in CARP.)

Gonul, M, Cakmak, SK, Soylu, S, Kilic, A, Gul, U, Ergul, G. “Successful treatment of confluent and reticulated papillomatosis with topical mupirocin”. J Eur Acad Dermatol Venereol. vol. 22. 2008. pp. 1140-2. (Bacterial infection may be the cause of CARP mupirocin may be effective for this reason.)

Katayama, I, Yokozeki, H, Nishioka, K. “Oral minocycline improved keratosis follicularis squamosa (Dohi) and reticulated disorders: Bacterial factors are possibly involved in aberrant keratinization”. J Dermatol. vol. 21. 1994. pp. 604-8. (This article discusses the possible bacterial pathophysiology of CARP.)

Henning, JP, de Wit, RF. “Familial occurrence of confluent and reticulated papillomatosis”. Arch Dermatol. vol. 117. 1981. pp. 809-10. (A case of familial CARP.)

Kägi, MK, Trüeb, R, Wüthrich, B, Burg, G. “Confluent and reticulated papillomatosis associated with atopy. Successful treatment with topical urea and tretinoin”. Br J Dermatol. vol. 134. 1996. pp. 381-2. (This article discusses alternate therapies for CARP.)

Kurkcuoglu, N, Celebi, CR. “Confluent and reticulated papillomatosis: response to topical calcipotriol”. Dermatology. vol. 191. 1995. pp. 341-2. (Calcipotriol for CARP.)

Hirokawa, M, Matsumoto, M, Iizuka, H. “Confluent and reticulated papillomatosis: a case with concurrent acanthosis nigricans associated with obesity and insulin resistance”. Dermatology. vol. 188. 1994. pp. 148-51. (This article discusses the possible link between insulin resistance and CARP.)

Stein, JA, Shin, HT, Chang, MW. “Confluent and reticulated papillomatosis associated with tinea versicolor in three siblings”. Pediatr Dermatol Jul-Aug. vol. 22. 2005. pp. 331-3. (This article indicates that tinea versicolor may co-exist in patients with CARP.)

Lee, SH, Choi, EH, Lee, WS, Kang, WH, Bang, DS. “Confluent and reticulated papillomatosis: a clinical, histopathological, and electron microscopic study”. J Dermatol. vol. 18. 1991. pp. 725-30. (This article delves into pathophysiology by detailing the microscopy of the disease.)